The present invention relates generally to dynamoelectric machines. More specifically, this invention relates to a stator winding for a dynamoelectric machine, in which the winding is a cascading winding.
Dynamoelectric machines, such as alternating current generators, or alternators, are well known. Prior art alternators typically include a stator assembly and a rotor assembly disposed in an alternator housing. The stator assembly is mounted to the housing and includes a generally cylindrically-shaped stator core having a plurality of slots formed therein. The rotor assembly includes a motor rotor attached to a generally cylindrical shaft that is rotably mounted in the housing and is coaxial with the stator assembly. The stator assembly includes a plurality of wires wound thereon, forming windings. The stator windings are formed of slot segments that are located in the slots and end loop segments that connect two adjacent slot segments of each phase and are formed in a predetermined multi-phase (e.g. three or six) winding pattern in the slots of the stator core.
A type of stator well known in the art is a high slot fill stator, which is characterized by rectangular shaped conductors that are aligned in one radial row in each slot and that fit closely to the width of the rectangular shaped core slots. High slot fill stators are advantageous because they are efficient and help produce more electrical power per winding than other types of prior art stators. These stators, however, are disadvantageous because the windings are typically interlaced, in which the wires are required to alternate outer and inner radial portions of each slot. These interlaced windings require an interlacing process to interlace the conductors of all the phases prior to inserting the winding into the core and therefore disadvantageously increase the complexity of placing the winding on the stator
A particular type of high slot fill stator is one that utilizes bi-filar windings. In a stator utilizing bi-filar windings, each phase turn includes two wires or filars which are connected in parallel. The wire cross section of each filar in a bi-filar design is half of that in a single filar design. Therefore, wires in bi-filar designs are much more structurally flexible for bending and turning at stator winding end turns. Bi-filar windings, however, are subject to overheating due to cross current circulation between filars. Cross current circulation can occur when the two filars are linked by a different amount of flux and therefore have different generated voltages. This can occur if the slot segments of the first filar have a different average radial position in the core slots than the slot segments of the second filar and a phenomenon known as magnetic flux slot leakage is present. One method developed to reduce the amount of cross current circulation is to alternate radial positions between the first and second filars at each end loop. This technique, however, is complicated and expensive to manufacture.